Predictable Delays Associated with VoIP Traffic

The bullet points below each type of constant or “predictable” delay encountered with VoIP traffic, and how these issues can be compensated for where possible.

Processing/Packetization Delay. Processing and packetization delays are a function of the time that it takes to actually create, code, compress, decompress, and decode packets. This is influenced by the codec(s) used on the network, as well as the use of specialized hardware or software during the coding process. For example, a DSP (hardware) will handle these processes more quickly than specialized software.

Serialization Delay. Serialization delay is the defined as the amount of time that it takes to physically place a frame onto a serial link. This is influence by both the size of a frame and the speed of a link, and is calculated by dividing the length of a frame by the bit rate. The faster the link and the smaller the frame, the lower the serialization delay. For example, the serialization delay associated with sending a 160 byte (1280 bit) frame across a 128 kbps would be 10 % or 10 ms (1280 bit frame divided by the 128,000 bps link speed).

Propagation Delay. Propagation delay is the amount of time that it takes for a signal to be propagated across a network between a sender and a recipient, and is calculated at a rate of 0.0063 km/s. Because physical laws and properties define it, the network designer cannot influence this type of delay.